This invention relates to an internal combustion engine and more particularly to an improved induction system for such engines which induction system is particularly adapted for use with four-cycle engines.
In many types of engines, the induction system includes, in addition the normal port control which communicates the intake passage with the combustion chamber, a check valve that is positioned upstream of the port control and which precludes reverse flow through the induction system. This type of arrangement is commonly used in 2-cycle engines, but also may be employed in four-cycle engines to achieve some of the same purposes. That is, in a 2-cycle engine, the port control of the intake port is achieved by the movement of the piston relative to the port. In a four-cycle engine, as is well known, the intake port is controlled by a valve that is operated in timed sequence with the engine crankshaft. However, with either type of engine, the use of a check valve may provide additional advantages in charging efficiencies because of its ability to preclude reverse flow.
Although the use of the check valves provides improved induction efficiency under some conditions, the resistance of the check valve to opening movement can, in some instances, restrict flow. Also, there is inertia in the intake system which must be overcome each time the check valve opens and closes and, thus, the air flow may be delayed from the time when the intake port is actually open.
It is, therefore, a principal object of this invention is to provide an improved induction system for an engine.
It is a further object of this invention to provide an improved induction system for engines embodying check valves in addition to the normal intake port control.
It is a further object of this invention to provide an arrangement wherein the flow through the intake passage may be continued even after the intake port is closed and when a check valve is in the induction passage.
In accordance with one feature of the invention, this latter effect can be achieved by providing a plenum chamber that is disposed between the check valve and the intake port. Thus, when the intake port is closed, the check valve may be retained open by the inertia of the airflow through the intake passage which existed at the time when the intake port closed. This inertial flow can then pass into the plenum chamber for introduction into the engine the next time the intake port is open. This obviously improves charging efficiency.
It is, therefore, a still further object of this invention to provide an improved induction system arrangement for an engine wherein a check valve is provided in the induction system, but flow past the check valve is permitted even when the intake port is closed.
Although it is possible to provide an additional and separate plenum chamber for the aforenoted purposes, it also is possible to employ the engine crankcase, if the engine is of the four-cycle type, as the actual plenum device.
It is, therefore, a still further object of this invention to provide such an induction system.
In addition to the improved induction of the engine by utilizing the crankcase chamber as a plenum chamber, still additional advantages can be enjoyed by using such an arrangement. For example, in addition to providing a volume into which the air can continue to flow when the intake port is closed, the crankcase chamber itself may act as a compressor. That is, when the piston is moving toward bottom dead center, the volume of the crankcase chamber is decreased. As a result of this, if the crankcase chamber is communicated with the intake passage, the charge compressed in the crankcase chamber can be delivered to the combustion chamber at an increased pressure. This provides, in effect, a supercharging function. However, under some circumstances, the increased pressure may be undesirable.
It is, therefore, a still further object of this invention to provide an improved induction system of this type wherein the crankcase chamber can act as a plenum chamber, but wherein an arrangement is incorporated for reducing the maximum pressure generated so as to avoid knocking and other objectionable loading on the engine.
It is well known that blow-by and crankcase ventilation gases tend to accumulate in the crankcase chamber. Systems have been provided for ventilating the crankcase chamber so as to avoid the build-up of these objectionable products in the crankcase chamber. This is desirable to ensure against oil contamination and also to ensure adequate ventilation for the engine. However, these crankcase ventilation gases and blow-by gases should not be discharged directly to the atmosphere.
There have been proposed, therefore, crankcase ventilating systems wherein the crankcase ventilating gases are delivered to the engine induction system. In this way, hydrocarbons and other objectionable crankcase ventilating gas components can be purified by combustion in the combustion chamber before they are discharged to the atmosphere. Frequently, the crankcase ventilation system delivers the crankcase ventilating gases to the induction system of the engine. Normally this is done at point upstream of the throttle valve and frequently into the air cleaner of the engine. However, this results in the possible discharge of crankcase gases to the atmosphere under at least some running conditions.
In accordance with a further object of this invention, the crankcase chamber is connected to the induction system in such a way as to achieve the aforenoted effects of improving charging efficiency, while, at the same time, providing an easy way in which the crankcase ventilation can be accomplished without the possibility of crankcase ventilating gases escaping to the atmosphere without having first been repassed through the combustion chamber.